Fuel cell power systems convert a fuel and an oxidant to electricity. One fuel cell power system type of keen interest employs use of a proton exchange membrane (hereinafter “PEM”) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as air/oxygen) into electricity. The PEM is a solid polymer electrolyte that facilitates transfer of protons from the anode to the cathode in each individual fuel cell of the stack of fuel cells normally deployed in a fuel cell power system.
In a typical fuel cell assembly (stack) within a fuel cell power system, individual fuel cells have flow fields with inlets to fluid manifolds; these collectively provide channels for the various reactant and cooling fluids reacted in the stack to flow into each cell. Gas diffusion assemblies then provide a final fluid distribution to further disperse reactant fluids from the flow field space to the reactive anode and cathode; these diffusion sections are frequently advantageously embedded as a part of the design of collector electrodes pressing against the reactive anode and cathode.
Effective operation of a PEM requires a balanced supply of water in the polymer of a PEM to maintain its proton conductivity while maintaining the flow field channels and gas diffusion assemblies in non-flooded operational states. In this regard, the hydrogen is supplied to the anode face of the MEA and reacts with the catalyst thereon to form hydrogen cations and free electrons. The oxidant, typically oxygen or oxygen-containing air, is supplied to the cathode face of the MEA and reacts with hydrogen cations that have crossed the proton exchange membrane to form water. Thus, the fuel cell generates both electricity and water through the electrochemical reaction, and the water is removed with the cathode effluent, dehydrating the PEM of the fuel cell unless the water is otherwise replaced. It is also to be noted that the inlet air flow rate to the cathode will generally evaporate water from the proton exchange membrane at an even higher rate than the rate of water generation (and commensurate dehydration of the PEM) via reaction at the cathode.
When hydrated, the polymeric PEM possesses “acidic” properties that provide a medium for conducting protons from the anode to the cathode of the fuel cell. However, if the PEM is not sufficiently hydrated, the “acidic” character diminishes, with commensurate reduction of the desired electrochemical reaction of the cell. Hydration of a fuel cell PEM also assists in temperature control within the fuel cell, insofar as the heat capacity of water provides a heat sink.
There is also a need to maintain the flow field channels and gas diffusion assemblies in a non-plugged state respective to any particulates which might be in the gaseous oxidant and fuel fluids which feed the cell; this concern is especially relevant to the oxidant in fuel cell power systems deployed on vehicles when the oxidant is air, since the condition of air varies from location to location, and the vehicle clearly has a purpose of providing transportation from location to location. As is generally appreciated, filters are traditionally used in vehicles to provide clean air to both fuel cells and, for that matter, to most internal combustion engines traditionally used to power vehicles.
There is also a need to provide thermal conditioning of feed gases to the fuel cell stack. In this regard, it is desirable to maintain the temperature of the feed gases within an operating range. However, the ambient conditions of the environment as well as the operating conditions of the fuel cell system may cause the feed gases to be outside of the desired temperature range.
In addition to issues in water balance, filtration and temperature conditioning of feed gases, another issue in fuel cell design for use in vehicles is directed to the efficient use of space. In this regard, space in a vehicle is precious and design approaches which represent an efficient use of space in the vehicle clearly benefit the utility of the vehicle; this leads toward integration of the humidifying system or gas conditioning system into each of the fuel cells, as provided.
Accordingly, there is a need for a fuel cell power system which includes full humidification of the feed gases (especially the oxidant), high capture filtration of particulates in the feed gases, and thermal conditioning of feed gases commensurate with full humidification, in such a way that a minimum of space is needed for the humidification, cooling and filtration operations.